1. Field of Invention
The invention relates to the field of emptying extracorporeal blood circulations after a hemodialysis treatment.
2. Description of the Prior Art
In a hemodialysis treatment, blood from a patient to be treated circulates in an extracorporeal circulation in which blood flows from a withdrawal point through an arterial blood line to the blood chamber of a hemodialysis machine divided by a semipermeable membrane into a blood chamber and a dialysis fluid chamber and through a venous blood line to a return point. The dialysis fluid chamber is in turn part of a dialysis fluid circulation in which dialysis fluid circulates as cleaning fluid. For this purpose, the commercial hemodialyzers usually have thousands of hollow fibers that have semipermeable walls. Blood flows through the interior of the hollow fibers while the dialysis fluid is fed into the fiber interspace, usually in the opposite direction from the blood, and is carried away. The elements of the extracorporeal blood circulation and the hemodialyzer are often provided only for a single use, whereas the connecting lines of the dialysis fluid circuit are normally reused.
The dialysis fluid has concentrations of blood constituents such as electrolytes corresponding approximately to those of a healthy person, so that the corresponding concentrations in the blood can be kept at a normal level. Substances such as creatinine or urea to be removed from blood are not present in the dialysis fluid, so these are removed from the blood by diffusion simply because of the concentration gradient on the membrane. With the help of a pressure gradient, excess water is withdrawn from the blood by convection and/or ultrafiltration.
Such processes are controlled by hemodialysis machines, which usually also ensure preparation of the dialysis fluid from water and concentrates so that it has the correct composition and temperature. At the same time, this equipment is increasingly capable of assuming a wide variety of monitoring functions of the hemodialysis treatment to minimize the risk to the patient and permit rapid countermeasures to be taken if there are complications.
At the end of the hemodialysis treatment, the extracorporeal blood circulation is first filled with the patient's blood. Since the volume of this blood is usually approximately 200 mL, which is a substantial quantity, this blood is returned to the patient after the end of the treatment. It is customary in this regard to first stop a pump that is arranged in the extracorporeal blood circulation and interrupt the vascular access at the withdrawal point, e.g., by removing the arterial cannula. Then the cannula itself is removed and the remaining arterial connection point is connected to a bag containing a physiological infusion solution, usually saline solution. Then operation of the blood pump is started again and the blood is conveyed back through the return point, which is still connected to the patient, whereupon the extracorporeal blood circulation is filled up with the infusion solution at the same time. If the phase limit between the blood and the infusion solution has reached the return point, the return process is concluded. Then after stopping the blood pump again, the connection of the venous blood line to the patient at the return point can be interrupted, for example, by pulling the venous cannula.
In this condition, the extracorporeal blood circulation is completely filled with fluid. The same thing is true of the dialysis fluid circulation and in particular also the dialysis fluid chamber of the hemodialyzer in which essentially dialysis fluid remains.
To dispose of the components of the extracorporeal circulation and the hemodialyzer, it is advantageous if these components are emptied of the liquid contained in them prior to being discarded. This is true to a particular extent of the two chambers of the hemodialyzer that contain most of the fluid. Emptying reduces the weight of the used disposable item, which is usually classified as special waste, and reduces the problem of pollution of the environment due to the fluid discharged.
WO 96/040313 A1 therefore proposes connecting the extracorporeal blood circulation to an air source of a hemodialysis machine after a disinfection step to replace the fluid with air in this area. In another embodiment, it is also proposed that the dialysis fluid circulation should be emptied by connecting it to the same air source. To empty the extracorporeal blood circulation, however, the arterial blood line must be connected to a disinfection port and the venous blood line must be connected to an outflow port, which necessitates additional operation steps. At the same time, it is important to be sure that there is no contamination of the hydraulics of the hemodialysis machine due to the directly closed extracorporeal blood circulation.
WO 01/051106 A1 describes a method in which the arterial and venous blood lines are not only in fluid connection through the blood chamber of a hemodialyzer but also are connected to form a ring. Fluid contained in the extracorporeal circulation is then circulated in the extracorporeal circulation with the blood pump running and is conveyed through the membrane of the hemodialyzer into the dialysis fluid circulation by a pressure gradient. An aeration opening may be provided on the venous air separator, permitting a resupply of air through an opened valve on reaching a certain suction pressure. This method also requires additional operation steps due to the additional use of the two blood lines and requires the use of other components such as connectors or even line elements.